Known diode-accessed, cross-point memory cells may use a rectifying diode as an access device to a state-changeable memory element. The memory element may contain chalcogenide phase change material. Applying a current to the memory element may change a phase of the material so that the memory element exhibits a different resistance. The phase may also be changed back. Hence, the two resistive states provide the “on” and “off” status for data storage.
FIG. 1 shows a conceptual, perspective view of a diode-accessed, cross-point memory array and illustrates its general spatial configuration. The simplified view of FIG. 1 merely shows a memory array 100 that includes words lines 102 having a direction orthogonal to a direction of bit lines 104 and overlapping at cross-points. At cross-points, an access diode containing a n-type material 106 and a p-type material 108 is combined with a memory element 110 in an electrically-connected series extending between word line 102 and bit line 104 at the cross-point. Actual structures implementing the concept shown in FIG. 1 may be formed by a variety of known methods.
To achieve a 4F2 footprint, where “F” is feature size of the access diode, some known methods form n-type material 106 and p-type material 108 in a monocrystalline silicon substrate. With the rectifying diode positioned in monocrystalline silicon, a high current density may be provided to effect a phase change in the state-changeable memory element 110 when it contains chalcogenide phase change material. Other silicon-based diodes may include those formed in polysilicon.
Unfortunately, forming silicon-based diodes uses processing temperatures in excess of 400° C. For activation annealing, temperature may be from 800° C. to 1000° C. for a time of from 2 hours to 20 seconds. As a result, structures of the memory array sensitive to temperatures in excess of 400° C. are formed in advance of processing the silicon-based diodes. Although silicon-based diodes may provide a high current density, their presence also limits the materials and processing order suitable for forming the memory array. Methods and/or materials that overcome the limitations of using silicon-based diodes may be useful.